This invention relates to a vehicle steering wheel attachment, by means of which the vehicle steering wheel is detachably arrested on a steering shaft.
In steering wheels which nowadays are usually equipped with gas bag modules, the steering wheel should detachably be arrested at the steering shaft, as steering wheels are completely exchanged after an accident. Due to the presence of the gas bag module it has become much more difficult to accommodate the attachment, as the accessibility from above is no longer existing.
The invention provides a vehicle steering wheel attachment which is distinguished by a simple structure and an extremely stable fixing. The vehicle steering wheel attachment which is proposed comprises a free end of a steering shaft which end has a multiple-cornered profile, i.e. a polygonal cross-section, the free end further having a radial groove including a wedge surface. The attachment further comprises a hub portion of the steering wheel, the hub portion including a multiple-cornered recess corresponding to the profile of the steering shaft and a radial guiding surface. A wedge is provided which can be moved along the radial guiding surface so as to be moved in and out of engagement with the groove. A drive screw is provided which is seated in a threaded bore in the hub portion and is rotatably coupled with the wedge. In the steering wheel attachment proposed, torque transmission is achieved via a multiple-cornered profile which can easily be produced. Axial fixing is effected by means of the wedge, which rests against the wedge surface and leads to an axial clamping of the hub portion on the steering shaft. By means of such axial clamping, any free motion between shaft and hub can be prevented.
The wedge also produces a large-surface abutment between steering wheel, wedge and hub portion, which provides an increased stability. Studs with a conical end, which have been used so far, cannot produce such stability.
The wedge preferably has a central bore in which an axial pin of the drive screw is rotatably accommodated, a safety means in the form of a separate part connecting the drive screw and the wedge in axial direction. Therefore, wedge and drive screw are different parts which can be made of different materials. The wedge does not rotate with the rotation of the drive screw.
The drive screw is radially directed towards the imaginary middle axis of the steering shaft, and preferably the resultant force exerted by the wedge on the steering shaft (graphically speaking the force vector) is radially directed towards the imaginary middle axis, too. Advancing the wedge does therefore not lead to a force component which might cause a peripheral rotation of the steering shaft relative to the hub portion.
Furthermore, the hub portion is preferably designed such that the wedge can axially be moved into the recess and via the recess can be placed against the guiding surface and subsequently be displaced radially. This possibility reduces the effort for manufacturing the hub portion, as mounting the wedge can be effected via the recess.
Not only mounting the wedge, but also connecting the wedge with the drive screw is effected via the recess. The steering wheel attachment is designed such that upon inserting the wedge the drive screw can be screwed into the threaded bore radially from the outside, and that via the axial recess in the hub portion the two parts are subsequently detachably connected with each other in a nondestructive way. This embodiment ensures that it is not necessary to provide extremely large, radially continuous guideways weakening the hub portion, which guideways provide for a radial insertion of the wedge from the outside through the entire hub portion. The guideway for the wedge has to be only so deep that the wedge can be retracted far enough, in order to allow a mounting and removal of the steering wheel from the steering shaft and to ensure that the two parts are fixed in the mounted condition.
In accordance with a preferred embodiment, the drive screw has a fine thread. Additionally or optionally, the drive screw or the threaded bore can be designed as self-locking screw connection. In accordance with the preferred embodiment, it is provided for this purpose that the drive screw has a threaded portion which has a nut in which a safety thread is inserted, which is deformed when the screw is screwed in and ensures the locking of the drive screw. With the design as fine thread and with the self-locking feature a high unscrewing moment and a high vibration resistance are obtained with very little effort. In addition, the self-locking feature is preferably realized such that a further assembly upon disassembly is possible without an exchange of parts.
In accordance with one aspect of the invention, a coding-for instance a projection engaging in a groove-is provided between the hub and the steering wheel. By means of this coding it is possible to mount the hub on the steering wheel in only one angular position.
In accordance with the preferred embodiment, the steering shaft has a conical surface at its free end, and to be more precise, the free end adjoins a conical surface at the steering shaft, which is formed relative to the wedge surface such that the hub portion is clamped between the wedge surface and the conical surface. The conical surface can thus be kept very large and in addition be used for centering hub portion and steering shaft.